What also caught my eye was Tom Marcus' description of how officers account for the period spent in MI5 when they've left the service and are applying for jobs; naturally former agents remain bound by the Official Secrets Act and must invent plausible cover stories. He told the BBC's Victoria Derbyshire programme that “some people come up with a Ministry of Defence cover story, but trying to explain the skills you say you have for a made-up story just unravels – and I wouldn't feel comfortable doing that.”
I was interested to read this, because the Ministry of Defence cover story is what James Bond of the novels uses. The first occasion seems to be in Diamonds are Forever (1956, chapter 3), when Assistant Commissioner Vallance introduces Bond to Inspector Dankwaerts as Commander Bond of the Ministry of Defence. In The Spy who Loved Me (1962, chapter 15), Bond gives the Ministry of Defence as his address in a letter to Vivienne Michel.
There are two references in On Her Majesty's Secret Service (1963). At the College of Arms, Bond tells Griffon Or that he's from the Ministry of Defence (chapter 6), and we learn that Sable Basilisk thought Bond was vaguely employed by the Ministry of Defence (chapter 8).
In his obituary of Bond in You Only Live Twice (1964, chapter 21), M identifies Bond as an officer of the Ministry of Defence, as does the Jamaican police commissioner in The Man with the Golden Gun (1965, chapter 16).
It's in the short story 'Octopussy' that Fleming describes the Ministry of Defence cover, used by Bond when greeting Major Dexter Smythe, as 'the hoary euphemism' for the Secret Service. In another short story, 'The Property of a Lady', Bond tells Fabergé expert Kenneth Snowman that he's from the Ministry of Defence.
In light of Tom Marcus' account, these occurrences raise some interesting points. One is that the Ministry of Defence cover story is a legitimate one, and its use in the Bond books may well reflect a reality of British Intelligence. In other words, the use of the Ministry of Defence as a front had currency when Ian Fleming was writing and remains current now.
Another point is that most Ministry of Defence references appear in the final few books. There is just one occurrence in the first nine books, but in the final five, there is at least one reference in each. It's not obvious why this should be the case, but possibly Fleming used the Ministry of Defence trope or meme to add authenticity to the stories. Also, with each successive use of the meme, the chances that Fleming would use it again in the next book increased.